Concretions in patients' bodies, for instance gall stones and in particular kidney stones, are only rarely removed surgically at present, but are predominantly destroyed in situ, after which the destroyed residues can be naturally evacuated. Various methods of destruction are known in this respect. The classical method, presently widely abandoned, consists of using mechanical crushing tongs. By means of highly complex large apparatus, the stone can be destroyed by using concentrated hydraulic waves ultrasonically generated outside the body and passing through the body. In another procedure, electro-hydraulic shock waves are generated in the immediate vicinity of the stone. Stones furthermore are destroyed using laser pulses or by contact with ultrasonic vibrators.
In recent years, mechanical destruction has been successful employing an impact wire to which are applied impact pulses. This impact wire is supplied with impact impulses at its proximal end by an impact generator, the impact impulse being a mechanical pulse having a very steep rise flank and causing compression of the proximal end of the impact wire, this compression propagating as an impact pulse through the wire and driving the distal end of the impact wire into axial extension, whereby the body's concretion within the excursion zone is easily destroyed. The required wire has a diameter, for instance, of 1-2 mm and a length, for instance, of 50 cm and is very easily inserted into the body, such as through the urethra of the patient as far as a urethral stone which is typically situated in the upper end region of the urethra.
In known apparatus of this kind, the impact pulse is generated at the proximal end of the impact wire by being hit by a mass shaped like a projectile and reciprocatingly driven in the longitudinal direction of the impact wire. According to European patent document B1 0,317,507, this projectile may be driven pneumatically.
Apparatus of this general type is known from German patent document A1 4,313,768. In this disclosure, the impact generator is electromagnetic. A stationary coil energized with current pulses accelerates a heavy mass designed as a magnetic core in the axial direction of the impact wire over a fairly substantial path until it impacts this wire with high momentum.
The last two above designs substantially offer the same advantages and incur the same drawbacks. They manage to generate impact pulses in impact wires, for instance 1-2 mm in diameter and made of spring steel, by being impacted by the mass, said pulses driving the distal end face of the impact wire into excursions of about 1 mm at speeds up to about 20 m/s in a manner suitable to destroy body concretions. However, this design suffers from the drawback of the impact principle, which entails high stress on the impact surface and commensurate maintenance. Moreover, the duration and intensity of impact is inherently not adjustable in the known apparatus. Only the impact speed of the mass and hence the intensity of impact can be controlled. Therefore, the shock pulses can be matched to requirements only in a very limited way. Again, this design entails a comparatively large and heavy impact generator which must be hand-held. This generator when in operation is fairly noisy and generates strong vibrations which are irksome during treatment.